California's drought has developed an interesting relationship between farmers and oilers: California oil wells produce more water than oil, and Chevron filters that water and sells it to a local water district. Interest in the technology is growing in the Central Valley, but high costs and uneasy relations between oil and agriculture might get in the way.

ROBERT SIEGEL, HOST:

California's historic drought means that many of the state's farmers are struggling to keep their crops alive this year. Reservoirs and wells are running dry. Yesterday on the program, we heard about how tensions are rising over water being used by the oil industry for hydraulic fracturing. Today, a plan to send water from oil extraction to farmers.

Lauren Sommer from member station KQED has the story.

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LAUREN SOMMER, BYLINE: Oil companies in California have a secret. Sure, they drill for oil but what they actually get is, with a just little bit of oil mixed in.

ABBY AUFFANT: That is a difference in California versus other states. The water is an issue in all of the fields.

SOMMER: Abby Auffant is showing me around Chevron's Kern River oil field, about two hours north of Los Angeles. The hills here are covered in pump jacks - almost 10,000 of them - slowing drawing oil and water out of the ground. That water is naturally found underground where the oil is.

AUFFANT: Where Kern River field produces its oil and its water from is basically a freshwater aquifer.

SOMMER: For every barrel of oil, they get nine barrels of groundwater. It adds up to millions of gallons a day, which creates a problem for oil companies: What to do with it? Many companies dispose of it long-term by pumping it back underground, where it's trapped in rock layers. But Chevron is trying something else.

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DAVID ANSOLABEHERE: The fact that we have this water coming in, it's a tremendous bonus.

SOMMER: David Ansolabehere is standing next to a 40-inch pipe that's gushing water. He's the general manager of the Cawelo Water District.

ANSOLABEHERE: We deliver water to about 45,000 acres which are nut trees, citrus and vineyards.

SOMMER: Chevron filters out the oil and sends the water to this reservoir. It makes up about a quarter of the water district's supply. Ansolabehere says it's their only reliable supply during the drought, because most of the other sources have been cut completely.

ANSOLABEHERE: It's going to be very tough. We're looking at just making sure the landowners can keep their trees alive this year.

SOMMER: Other Central Valley water districts are in the same boat, which is why Ansolabehere says there's been a lot of interest in this project.

ANSOLABEHERE: Lately it's I've been getting a lot of phone calls, meeting with people that want to do the same type of thing.

SOMMER: Oil and agriculture have long been neighbors in this part of the state. California is the largest producer of food in the country and it's the third largest oil producer. So it hasn't been lost on farmers that while their water supplies are going dry this year, the industry next door is swimming in billions of gallons.

TUPPER HULL: You have tremendous water resources that are a byproduct of oil production.

SOMMER: Tupper Hull is with the Western States Petroleum Association, an oil industry group.

HULL: It's very conceivable that, in the very near future, oil production could be net provider of water for California Ag and other purposes, as opposed to a consumer.

SOMMER: The oil industry is a consumer because it uses fresh water for the controversial oil extraction technique known as hydraulic fracturing, or fracking. Recycling water would offset that use. But duplicating Chevron's project in other parts of the state isn't that simple. First, water from the oil field is salty, so the water district has to mix it with freshwater until it's good enough for farms. Also...

KASSIE SIEGEL: One of the problems they've seen at that project is very high arsenic levels in the water.

SOMMER: Kassie Siegel is with the Center for Biological Diversity, an environmental advocacy group. She says until a few years ago, Chevron used to release water into a creek in the winter, when demand from farmers was low. That water wasn't diluted and the company was fined for violating limits on arsenic.

SIEGEL: It just shows again that there's no safe way to deal with the oil and gas wastewater. Every single method that has been proposed and used has real risks and health harms associated with it.

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SOMMER: Elsewhere in the country, water used in oil and gas production is cleaned up through a treatment process. That happens in Pennsylvania, where it's recycled in fracking operations. Chevron's Abby Auffant says water from other California oil fields would need to be treated too, because of higher levels of contaminants, but it's expensive.

AUFFANT: If we were able to identify a cost-effective manner in which to treat the water, it's certainly something that we would be interested in.

SOMMER: As expensive as the water would be, it looks more cost-effective in a drought year like this one. Water prices are already sky-high and California farmers are facing a long, dry summer ahead.

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